An optical network system mainly includes SDH (Synchronous Digital Hierarchy)/Sonet (Synchronous Optical Network), wavelength network and so on. Conventional optical network is a network system based on centralized management, and information intercommunication is performed via permanent connection between the nodes in the network. Permanent connection means that the service switching relations between all the nodes are manually configured in a conventional optical network system, and once this configuration is determined, it will generally not be modified in a large-scale optical network system; such a service switching relation between nodes is referred to as permanent connection.
Connection path in permanent connection mode is pre-calculated by the management plane according to the requirements of service switching between the nodes and the utilization of network resource etc.; then a cross-connection command is sent to each node via a network management interface along the connection path obtained from the calculation, and a connection path is established finally. Permanent connection mode is effectively used in the early stage of the development of optical network due to its advantages such as simple design and low cost. However, since manual work or network management system is needed during the establishment, maintenance and dismantlement process of a connection path in permanent connection mode, the operation process is very tiresome. As the data traffic of a network system increases continuously, this connection mode can no longer meet the requirements of dynamic flexibility of optical network systems.
Therefore, ITU-T (ITU-Telecommunication Standardization Sector) puts forward an ASON (Automatically Switched Optical Network) architecture. Two novel connection modes are introduced into ASON: soft permanent connection mode and switched connection mode. Wherein, the soft permanent connection mode is initiated by management plane, in which the connection path is established in control plane; the switched connection mode is initiated by user equipment, in which the connection path is established in control plane.
Wherein, the main characteristic of ASON architecture lies in that a control plane (control plane is a control communication network based on IP technology, and routing protocol, signaling protocol and so on can be operated on this network system to realize the automatic control on various services) is added in a conventional optical network, and a switched connection concept is put forward. Thus, a node in an ASON obtains the connection relation with other nodes via the partial-link detection technology at first, then issues its node and link status via the control plane and receives the status information issued by other nodes in the network, thus a “network map” describing the accurate topology information of the whole network can be obtained by each node in the network finally. In this “network map”, various information, such as node, link and resource, etc., is included. When a user equipment or a management plane requires a node to establish a connection path, the corresponding node obtains a feasible path with the “network map” information obtained and according to a certain routing algorithm (usually, CSPF (Constrained Shortest Path First) algorithm will be selected), then each node on the path is driven to establish a cross-connection relation with a signaling protocol (usually, RSVP-TE (Resource Reservation Protocol-Traffic Engineering) will be selected), thus a connection path will be established. When a network connection is dynamically established, dismantled or when link resource is changed due to a failure, the corresponding node will issue the information such as node and link status, etc. after the change, so that the inter-node “network map” can be updated synchronously.
In ASON, each node collects the “network map” information with Link Status Protocol which is applicable in a small-scale network. But, as the scale of ASON gets larger and larger, the network will be divided into a plurality of small control domains logically. As the network scale is further enlarged, each control domain divided is further divided, and finally a hierarchical ASON is formed.
The process of establishing a connection path in a control domain after the ASON is divided into a plurality of control domains is the same as that before the ASON is divided. However, when an end-to-end connection path across a plurality of control domains is to be established, a cross-domain connection path cannot be computed or established only according to the “network map” information in the current domain, because each control domain is independent to each other, and the nodes in each control domain only know the “network map” information in the current domain, rather than the “network map” information in other control domains. Therefore, in a hierarchical ASON, hierarchical routing is usually employed to establish a cross-domain connection path. During the process in which a cross-domain connection path is established using hierarchical routing, for each high layer control domain, the control domain of the lower layer is abstracted as a node, and the domain-to-domain links between the control domains of the lower layer are regarded as links between abstract nodes, and the intra-domain links between the internal nodes of a control domain of the lower layer is invisible to the control domain of high layer. In the control domain of high layer, the similar process as mentioned above is employed to diffuse the status information of links between each abstract node, so that each abstract node in the control domain of the current layer can obtain the network topology information of the current layer, i.e., the “network map” information of the current layer.
As the hierarchical ASON technology becomes more and more mature, it has been a problem as to how to identify the domain-to-domain link between each control domain of each layer, so as to diffuse the domain-to-domain link information of the current layer to the control domain of the higher layer correctly.
The inventor has put forward a method for identifying domain-to-domain links between each control domain of ASON in CN Application No. 200410073746.1, titled “A Method For Finding A Link Type”, the main process of which is shown as follows:
The identifier of the control domain to which a network node pertains is set in the node;
Each node sends the identifier of the control domain to which it pertains to an opposite terminal node during the negotiation process to establish a control channel between the nodes;
After each node receives the identifier of the control domain to which the opposite terminal node pertains sent by the opposite terminal node, it determines whether the identifier of the control domain to which the opposite terminal node pertains is the same as the identifier of the control domain to which the node itself pertains; if yes, it is determined that the node belongs to the same control domain as the opposite terminal node, and the link between the node and the opposite terminal node is an intra-domain link; otherwise, it is determined that the node and the opposite terminal node belong to different control domains, and the link between the node and the opposite terminal node is a domain-to-domain link; and
Each node rep orts the above obtained link type information to the routing protocol.
Referring to FIG. 1, it is a schematic diagram showing the simple topology in which the method of the prior application is used to determine whether a link is a domain-to-domain link. As shown in FIG. 1, area 1 represents a control domain of the bottom layer, wherein area 1 is consisted of node a, node b and node c, and it can be found that link A is a domain-to-domain link with the method of the prior application filed by the applicant. At the same time, the information about domain-to-domain link B and domain-to-domain link C can also be obtained by node a from the node status information diffused from node b and node c. Thus, in addition to the intra-domain links between ab, ac and bc, three domain-to-domain links A, B and C can also be obtained on node a in area1. Similarly, the corresponding link type information can also be obtained on node b and node c in area1.
However, in a hierarchical ASON (more than 2 hierarchies), it is required not only to identify the domain-to-domain links in the bottom layer between node a, node b and node c shown in FIG. 1, but also to identify the domain-to-domain link information of the abstract node abstracted by the control domain area1 in which node a, node b and node c exist in the control domain of the higher layer. As shown in FIG. 1, there are three links A, B and C in the control domain of the higher layer for the abstract node abstracted by area1, wherein in the control domain of the higher layer, link B and link C are intra-domain links, and link A is a domain-to-domain link. However, in the method of the prior application filed by the applicant, only the domain-to-domain link and the intra-domain link types for each node in the control domain of the bottom layer can be identified, but the domain-to-domain links between abstract nodes in each layer of control domain in a hierarchical ASON with more than two hierarchies cannot be identified. Therefore, in a hierarchical ASON with more than two hierarchies, the control domain of the lower layer cannot identify the domain-to-domain link information between the nodes in the control domain of the current layer, so the domain-to-domain link information between each node of the current layer cannot be diffused to the control domain of the higher layer.